194 Thus, _A. Young_, Travels in France I, 293 ff., has defined, with approximate accuracy, the limits within which the vine, maize and the olive grow. And so _von Cancrin_, Dorpater Jahrbuch IV, 1, distinguishes the ice zone, the reindeer-moss (a lichen on which the reindeer live in winter) zone, the forest zone, the zone within the limits of which cattle are raised; that in which the culture of rye begins, that in which it becomes permanent; the wheat, fruit-tree, vine, maize, olive, sugar cane and silk-worm zones. The United States are divided into cattle-raising, wheat-raising, cotton-raising, rice-raising and sugar-raising zones. Even in Europe, beyond the 60th parallel of north latitude, wheat can scarcely be cultivated; the polar limits of rye raising extend, at most, six or seven degrees farther. Towards the north, barley extends sometimes as far as the 70th degree. Here agriculture almost ceases, and the inhabitants are compelled to confine themselves to animal substances for food. On the other hand, these three cereals are not adapted to a tropical climate, while the bread-fruit tree, for instance, does not thrive at more than 22 degrees from the Equator, nor the banana at more than 35. Compare _Grisebach_, Die Vegetation der Erde nach ihrer klimatischen Anordnung. II, 1871. 195 Thus rye and wheat thrive in many parts of Siberia (Iakutzk) at an annual temperature of - 7.50, while in Iceland no cereals ripen at an annual temperature of + 4°. But in the former place the summer heat is + 16.2°; the winter cold, - 39.2°; in Iceland, + 12° and - 1.6°. In England, the myrtle, laurel, camelia and fuchsia stand the winter well; while the vine no where ripens. On the other hand, Astrakan and Hungary are vine growing countries, although the former is as cold in winter as North Cape, and although the cold is more intense in Hungary than in the Faroe Islands, where neither the oak nor the beech grow any longer. No good wine is produced on the western coast of France, north of 47° 20’ north latitude; in Champagne, north of 49°, or in the Rheingau, north of 51°. In Norway, the average heat is greater on the coast than in the heart of the country where, however, grain ripens, while it does not on the coast; for the mildness of the winter, no matter how great, can make no compensation for the want of heat. On the other hand, the cattle on the coast can remain much longer out of doors, and the sea seldom freezes in such a way as to interfere with the fisheries. _Blom_, Norwegen I, 39. _Boussingnault_ (Economie rurale considérée dans ses Rapports avec la Chimie, II) has made some interesting attempts to calculate by a mathematical process the amount of heat